1. Field of the Invention
The present invention relates to a method of manufacturing a liquid crystal display device (LCD), and particularly to a method of manufacturing an active matrix type liquid crystal display device using a semiconductor thin film (hereinafter referred to as an AM-LCD). The present invention can be applied to an electrooptical device equipped with such a display device.
Incidentally, in the present specification, the term xe2x80x9csemiconductor devicexe2x80x9d indicates all devices which function by using a semiconductor. Thus, the foregoing display device and the electrooptical device are included in the category of the semiconductor device. However, in the present specification, for facilitation of the distinction, terms such as a display device and an electrooptical device are selectively used.
2. Description of the Related Art
In recent years, a projector or the like using the AM-LCD as a projection type display has been vigorously developed. Moreover, the demand of the AM-LCD as a direct viewing display for a mobile computer or a video camera is also increasing.
FIGS. 2A and 2B schematically shows a structure of a pixel matrix circuit in a conventional active matrix type display device. Incidentally, the pixel matrix circuit is such a circuit that thin film transistors (TFTs) for controlling an electric field applied to a liquid crystal are arranged in matrix, and constitutes a picture image display region of the AM-LCD.
FIG. 2A is a top view showing the pixel matrix circuit seen from the above. Here, regions surrounded by a plurality of gate lines 201 provided in the horizontal direction and a plurality of source lines 202 provided in the vertical direction become pixel regions. A TFT 203 is formed at each of the intersections of the plurality of gate lines 201 and the plurality of source lines 202. A pixel electrode 204 is connected to each of the TFTs.
Thus, the pixel matrix circuit is constituted by the plurality of pixel regions formed in matrix by being surrounded by the plurality of gate lines 201 and the plurality of source lines 202, and the TFT 203 and the pixel electrode 204 are provided at each of the pixel regions.
FIG. 2B shows the structure of a section of the pixel matrix circuit. In FIG. 2B, reference numeral 205 denotes a substrate having an insulating surface, 206 and 207 denote pixel TFTs formed on the substrate 205, which correspond to the TFTs 203 shown in FIG. 2A.
The pixel TFTs 206 and 207 are connected to pixel electrodes 208 and 209, respectively. The pixel electrodes 208 and 209 correspond to the pixel electrodes 204 shown in FIG. 2A. The pixel electrodes 208 and 209 are generally obtained by patterning one metal thin film.
Thus, in the pixel matrix circuit of the conventional structure, boundary portions of electrodes (hereinafter simply referred to as boundary portions) 210 and 211 always exist between the pixel electrodes. That is, a difference in level, which corresponds to the film thickness of the pixel electrode, is inevitably formed. Poor orientation of a liquid crystal material occurs at such a difference in level, so that a displayed picture is disturbed. Besides, diffused reflection of incident light at the portion of the difference in level causes the contrast to lower or the efficiency of utility of light to lower.
As is apparent from FIG. 2B, the pixel electrodes 208 and 209 formed over the semiconductor elements or the intersections of the respective wiring lines have the state reflecting the shape of the semiconductor elements and the intersections. Such a difference in level also causes the foregoing problems.
Particularly, in a projection type display used for a projector or the like, since an extremely minute small display of about 1 to 2 inches in size is enlarged and projected, the foregoing problems become tangible.
In regard to the above described problems, a black mask (or a black matrix) has been conventionally used to shade the region where a picture image is disturbed, so that the ratio of contrast is increased. In recent years, since miniaturization of a device has been progressed and the controllability of a shading region for the purpose of a high aperture factor has been required, the structure in which the black mask is provided at a TFT side substrate has become the main stream.
However, in the case where the black mask is provided at the TFT side substrate, there arises various problems such as increase of patterning steps, increase of parasitic capacitance, and lowering of an aperture factor. Because of such circumstances, it is desired to achieve a technique by which the ratio of contrast can be assured without causing the above described problems.
An object of the present invention is therefore to solve the above-mentioned problems and to provide means for forming an extremely fine active matrix type display device by a simple process.
In order to achieve the above object, according to one aspect of the present invention, a method of manufacturing a semiconductor device comprises the steps of: flattening an insulating film formed on a substrate having an insulating surface; forming a plurality of electrodes on the insulating film; forming an insulating layer covering the plurality of electrodes; and flattening the surfaces of the plurality of electrodes and the surface of the insulating layer so that both the surfaces form the same plane, and boundary portions of the plurality of electrodes are filled with the insulating layer, wherein the flattening step is carried out with a precision of not larger than 20% of a thickness of the electrodes.
According to another aspect of the present invention, a method of manufacturing a semiconductor device including at least a first substrate, a transparent second substrate, and a liquid crystal layer held between the first substrate and the second substrate, the method comprising the steps of: flattening an insulating film formed on the first substrate; forming stripe-shaped electrodes on the insulating film; forming an insulating layer covering the stripe-shaped electrodes; and flattening the surfaces of the stripe-shaped electrodes and the surface of the insulating layer so that both the surfaces form the same plane, and boundary portions of the stripe-shape electrodes are filled with the insulating layer, wherein the flattening step is carried out with a precision of not larger than 20% of a thickness of the electrodes.
According to still another aspect of the present invention, a method of manufacturing a semiconductor device comprises the steps of: forming a plurality of semiconductor elements on a substrate having an insulating surface; forming an interlayer insulating film; flattening the interlayer insulating film; forming pixel electrodes electrically connected to the semiconductor elements on the interlayer insulating film; forming an insulating layer covering the pixel electrodes; and flattening the surfaces of the pixel electrodes and the surface of the insulating layer so that both the surfaces form the same plane, and boundary portions of the pixel electrodes are filled with the insulating layer, wherein the flattening step is carried out with a precision of not larger than 20% of a thickness of the electrodes.
According to still another aspect of the present invention, a method of manufacturing a semiconductor device including at least a substrate having a plurality of semiconductor elements formed in matrix and a plurality of pixel electrodes respectively connected to the semiconductor elements, and a liquid crystal layer held on the substrate, the method comprising the steps of: forming an interlayer insulating film; flattening the interlayer insulating film; forming pixel electrodes electrically connected to the semiconductor elements on the interlayer insulating film; forming an insulating layer covering the pixel electrodes; and flattening the surfaces of the pixel electrodes and the surface of the insulating layer so that both the surfaces form the same plane, and boundary portions of the pixel electrodes are filled with the insulating layer, wherein the flattening step is carried out with a precision of not larger than 20% of a thickness of the electrodes.
In the above-mentioned structure, a typical example in which a liquid crystal layer is held, is such a structure that a liquid crystal layer is held between a substrate (first substrate) including a plurality of pixel electrodes and an opposite substrate (second substrate) facing the first substrate. There can be a case where the second substrate is not required since, when a PDLC (Polymer Diffusion Liquid Crystal) is used for a liquid crystal layer, the liquid crystal layer itself is solidified.
Although a thin film transistor (TFT) is typical for a semiconductor element, other semiconductor elements such as an insulated gate field effect transistor (IGFET), a thin film diode, a MIM (Metal-Insulator-Metal) element, and a varistor element may be used.
If the flattening is made within 20% of the thickness of the electrode, it is possible to suppress the influence of unevenness to the thickness of the liquid crystal layer. Especially, in the case of a reflection type liquid crystal panel, since poor display due to the unevenness of the thickness of the liquid crystal layer becomes tangible, it is effective to use the present invention disclosed in the present specification.
In general, the film thickness of a pixel electrode is about 100 to 300 nm. Thus, it is appropriate that the flatness of the insulating film or the oriented film is restricted to not larger than about 20 to 60 nm. For example, in the structure as shown in FIG. 12, it is appropriate that the value indicated by xe2x80x9caxe2x80x9d or xe2x80x9cbxe2x80x9d is made 20 to 60 nm.
Although it is preferable that the flattening is restricted within 20% of the thickness of the pixel electrode, in practical viewpoint, it is effective even if the flattening is restricted within 50% of the pixel electrode.
As to the degree of flatness, assuming that the surface state as shown in FIG. 13 is obtained, it is appropriate to realize such flatness that the value of xcex80 is not larger than 15xc2x0. By doing so, it is possible to effectively use the light reflected by a reflecting pixel electrode formed thereon in optical modulation. Of course, in the state shown in FIG. 13, it is important to make the value of xe2x80x9ccxe2x80x9d not larger than 20 to 60 nm.
As a desirable limiting condition of parameters indicating the degree of flatness, as shown in FIG. 14, it is effective to make the condition that the amount of light reflected by the reflecting surface of a reflecting electrode is not smaller than 70% (with respect to the amount of incident light) in the cone with an inclination angle of 15xc2x0 with respect to the direction of an optical axis.
If these limiting conditions are combined with other parameters, they become more effective. That is, if the flatness is secured so as to satisfy the limiting conditions of these parameters or conditions regulated by the combination of limiting conditions of the respective parameters, more excellent effects of the present invention can be obtained.